Certain semi-automatic and automatic firearms, such as the family of AR-15/M16 rifles, operate with a gas operating system in which hot propellant combustion gas from a fired cartridge is made to operate the bolt carrier to cycle the action of the firearm.
The gas operating system of an AR-15/M16 rifle may be a direct gas impingement system, or a gas operated piston system. The direct gas impingement system directs hot propellant combustion gas from a fired cartridge directly to a bolt carrier to cycle the action of the firearm. More particularly, the gas pressure of the combustion gas pushes the bolt carrier rearward against the bias of a buffer spring, during which time the fired cartridge case is extracted from the chamber of the barrel and ejected from the firearm. As the gas pressure dissipates, the compressed buffer spring then decompresses and pushes the bolt carrier forward, during which time an unfired cartridge is removed from the magazine and loaded into the chamber of the barrel. In contrast to a direct gas impingement system, with a gas operated piston system, the gas forces a piston rod of a piston and the bolt carrier rearward to handle the extraction and ejection process, and thereafter the bolt carrier is forced forward by a decompression of the buffer spring to the closed position just as with direct impingement.
Operation of semi-automatic and automatic firearms, including operation of the AR-15/M16 family of rifles, is well known and described, for example, in U.S. Patent Application Publication No. US2012/0137872, the teachings of which are hereby incorporated herein by reference.
Certain shotguns may be operated with either a semi-automatic reload system or a manual pump-action reloading system. With a manual pump-action reloading system, rather than the reloading system being operated by gas from a fired cartridge, actuation of the reloading system is performed manually by the operator (shooter) of the shotgun. For both the semi-automatic and pump-action shotguns, shotgun shells are generally stored in a tubular magazine beneath the barrel, which is not detachable from the shotgun such that the shotgun may be operated with the use of multiple magazines.